Cable gels for optical fibre cables

ABSTRACT

Cable gels contain, in addition to polypropylene glycol and polyol, from 1 to 15 wt. % of a compressed fumed silica which has been rendered hydrophobic with silicone oil.

The invention relates to cable gels.

It is known to use thixotropic cable gels as filling material in opticalfibre cables.

DE 36 22 211 describes a filling material which contains from 50 to 99wt. % polypropylene glycol, especially having a molar mass from 2000 to3500, and from 50 to 1 wt. % highly disperse silicon dioxide asthixotropic agent.

U.S. Pat. No. 4,701,016 describes a filling material which contains from77 to 95 wt. % of an oil or of a mixture of oils and from 2 to 15 wt. %colloidal particles. They may additionally contain up to 15 wt. % of anelastomer. There are used as oils paraffin oil, naphthenic oil,polybutene oil, triglyceride-based vegetable oil, polypropylene oil,chlorinated paraffin oil and polyesters. The colloidal particles consistof hydrophobic fumed silica, precipitated silica and clay.

In U.S. Pat. No. 5,348,669 there is described a filling material whichcontains from 75 to 95 wt. % of a polypropylene glycol having a molarmass of at least 3000, and from 2 to 20 wt. % of either a hydrophilic orhydrophobic fumed silica. The filling material may additionally containan antioxidant in order to improve temperature resistance, and anelastomer in order to reduce oil separation.

U.S. Pat. No. 5,433,872 describes a filling material which contains from75 to 95 parts of a liquid to semi-solid polyol having a molar mass ofat least 4000, small amounts of an unsaturated compound, and from 1 to15 wt. % of a fumed silica as thickener. The filling material mayadditionally contain a thermoplastic elastomer in order to reduce oilseparation.

DE 38 39 596 describes a thixotropic gel and its preparation based on asynthetic hydrocarbon oil and a hydrophobic thixotropic agent. The cablegel is suitable as filling material in the production of optical fibrecables.

It is also known from the series of documents Pigmente No. 63, DegussaAG, 1995, page 28 to 30, that compressing hydrophilic fumed silicaenables the silica to be incorporated into the binder more rapidly, forexample using a planetary mixer or a planetary dissolver. Incorporationis understood to be the time required until the finely divided silicahas disappeared completely from the surface of the binder and is wettedwith the binder. Depending on the size of the batch, the dispersingdevice and the recipe, the incorporation time can be up to several hoursand is accordingly the step that determines the speed of production ofthe product in many applications. Furthermore, because of the increaseddensity of the silica, reduced dust formation of the silica is achieved.The smaller volume of the compressed silica can also be of advantagewhen planning the system of dispersing devices.

It is a disadvantage that the viscosity of the silica-containing binderfalls in most applications as the tamped density increases. Likewise,the dispersibility of the silica deteriorates. A phenomenon whichmanifests itself in the form of stippling, for example, in the case of asilicone sealing composition and higher surface roughness. Both effectsare significant disadvantages. For that reason, compressed hydrophilicfumed silica can be used only in relatively limited fields ofapplication.

Accordingly, the object is to produce cable gels in which thosedisadvantages do not occur.

The invention provides cable gels which are characterised in that theycontain, in addition to polypropylene glycol and polyol, from 1 to 15wt. % of a compressed fumed silica which has been rendered hydrophobicwith silicone oil.

The silica used can have a tamped density of from 60 to 150 g/l.

Fumed silicas are known from Ullmann's Enzyklopädie der technischenChemiei 4th edition, Volume 21, page 464 (1982).

The pyrogenically prepared silica can be rendered hydrophobic by meansof silicone oil in a known manner. For example, the following silicasmay be used as the pyrogenically prepared silicas which have beenrendered hydrophobic with silicone oil:

-   -   AEROSIAL® R 202 VV 60    -   AEROSIL® R 202 VV 90.

The physicochemical data of those silicas are listed in Table 1: TABLE 1AEROSIL AEROSIL R202 VV60 R202 VV 90 Behaviour towards hydrophobichydrophobic water Appearance loose white powder BET surface area¹⁾ m²/g100 +− 20 100 +− 20 Average primary particle size nm 14 14 Tampeddensity g/l 60 90 approx. value²⁾ Loss on drying³⁾ % <0.5 <0.5 Ignitionloss⁴⁾⁶⁾ % 4-6 4-6 C content % 3.5-5.0 3.5-5.0 pH value⁵⁾   4-6⁹⁾  4-6⁹⁾ SiO₂ ⁷⁾ % >99.8 >99.8 Al₂O₃ ⁷⁾ % <0.05 <0.05 Fe₂O₃ ⁷⁾ % <0.01<0.01 TiO₂ ⁷⁾ % <0.03 <0.03 HCl⁷⁾⁸⁾ % <0.025 <0.025 Drum size kg 10 15¹⁾following DIN 66131²⁾following DIN ISO 787/XI, JIS K 5101/21³⁾following DIN ISO 787/II, ASTM D 280, JIS K 5101/21⁴⁾following DIN 55921, ASTM D 1208, JIS K 5101/21⁵⁾following DIN ISO 787/IX, ASTM D 1208, JIS K 5101/24⁶⁾based on material dried for 2 hours at 105° C.⁷⁾based on material ignited for 2 hours at 1000° C.⁸⁾HCl content is a constituent of the ignition loss⁹⁾in water:ethanol = 1:1

In a preferred embodiment of the invention, a silica known from documentDE 199 61 933 A1 can be used.

Using that silica it is possible according to the invention markedly toshorten the time required for the production of the cable gel comparedwith an uncompressed fumed silica rendered hydrophobic with a siliconeoil, while the rheological and application-related properties of thethixotropic cable gel remain equally as good. This saving in terms oftime when producing the cable gel enables the costs to be reduced. Afurther advantage achieved with that more highly compressed fumed silicais reduced dust formation during incorporation into the binder.

It is surprising according to the invention that the compressed fumedsilica which has been rendered hydrophobic with a silicone oil ismarkedly different from the compressed hydrophilic fumed silica asregards Theological and application-related parameters. There is thus noappreciable fall in the viscosity of a cable gel as the degree ofcompression of the hydrophobic silica increases. Nor is there anydeterioration in other application-related parameters of the cable gel,such as, for example, oil separation. Incorporation of the compressedhydrophobic silica into the polypropylene glycol of the cable gel ismarkedly shorter than in the case of an uncompressed hydrophobic silica.Accordingly, the cable gel can be produced in a shorter time. This meansan improvement to the prior art. Further advantages which are obtainedwith the use of a compressed hydrophobic silica are, as in the case ofcompressed hydrophilic silicas, reduced dust formation duringincorporation into the binder.

The cable gels according to the invention can be used in the productionof glass fibre cables.

EXAMPLES

Irganox L 57 and Irganox L 135 are used as antioxidants.

Irganox L 57 is: CAS Number Product name Content Symbols R sets068411-46-1 Aniline, N- >99% N R 51/53 phenyl-, reaction products with2,4,4- trimethylpentene 000122-39-4 Diphenylamine <1% N-T R 23/24/25 - R33 - R 50/53

Irganox L 135 is a high molecular weight liquid antioxidant of theformula

Example 1

Production of cable gels using a dissolver and AEROSIL® R 202 andAEROSIL® R 202 VV 90

Recipe: 89.3 wt. % polypropylene glycol having a molar mass of 3850g/mol.  1.4 wt. % Irganox L57 (2 parts) and Irganox L135 (1 part) in theform of a mixture  9.3 wt. % AEROSIL ® R 202 or AEROSIL ® R 202 VV 90Procedure:

The polypropylene glycol is placed into the container of the dissolver.The antioxidant Irganox is added with gentle stirring. The silica isadded in portions with gentle stirring, and the incorporation time ismeasured until the silica has disappeared completely from the surface ofthe polypropylene glycol and is completely wetted with the polypropyleneglycol. Dispersion is then carried out in vacuo for 10 minutes at 3000rpm.

After 1 day's storage at room temperature, the viscosity of the cablegel is measured using a cone/plate rheometer at 23° C. and 20/s.

Likewise after storage of the cable gel for 1 day, the oil separation ofthe cable gel is measured by the following wire cone method: The cablegel is introduced by means of a spatula, as far as possible withoutbubbles, into a nickel wire cone (60 mesh sieve) and suspended over aglass beaker by a wire. The glass beaker is placed in an oven at 80° C.for 24 hours. The oil separation of the cable gel, i.e. the pure oilthat has dripped onto the bottom of the glass beaker during storage athigh temperature, is determined gravimetrically by re-weighing and isindicated in percent.

Results: Incorporation Viscosity in Oil separation Description time in sPa s in % Cable gel 81 23.9 0.65 with AEROSIL ® R 202 Cable gel 36 23.30.77 with AEROSIL ® R 202 VV 90Evaluation:

The incorporation time when AEROSIL® R 202 VV 90 is used is markedlyshorter than when AEROSIL® R 202 is used, with almost identicalviscosities and identical oil separations. Production of the cable gelcan therefore be shortened by using AEROSIL® R 202 VV 90.

Example 2

Production of cable gels by means of a 3-roller mill using AEROSIL® R202, AEROSIL® R 202 w 90 and AEROSIL® 200

Recipe: 89.1 wt. % polypropylene glycol having a molar mass of 2700g/mol.  1.4 wt. % Irganox L57 (2 parts) and Irganox L135 (1 part) in theform of a mixture  9.5 wt. % AEROSIL ® R 202 or AEROSIL ® R 202 VV 90 orAEROSIL ® 200Procedure:

The polypropylene glycol is placed into the container of the dissolver.The antioxidant Irganox is added with gentle stirring. The silica isadded in portions with gentle stirring, and the incorporation time ismeasured until the silica has disappeared completely from the surface ofthe polypropylene glycol and is completely wetted with the polypropyleneglycol. The cable gel is then milled twice in each case by means of a3-roller mill.

After 1 day's storage at room temperature, the viscosity and the flowlimit are measured using a cone/plate rheometer at 23° C. and 20/s.Likewise after storage of the cable gel for 1 day, the oil separation ofthe cable gel is measured by the following wire cone method: The cablegel is introduced by means of a spatula, as far as possible withoutbubbles, into a nickel wire cone (60 mesh sieve) and suspended over aglass beaker by a wire. The glass beaker is placed in an oven at 80° C.for 24 hours. The oil separation of the cable gel, i.e. the pure oilthat has dripped onto the bottom of the glass beaker during storage athigh temperature, is determined gravimetrically by re-weighing and isindicated in percent.

Results: Oil Incorporation Flow limit Viscosity separation Descriptiontime in s in Pa in Pa s in % Cable gel with 16 154 22.7 2.0 AEROSIL ® R202 Cable gel with 8 122 20.0 2.1 AEROSIL ® R 202 VV 90 Cable gel with28 0.01 35 97 AEROSIL ® 200Evaluation:

AEROSIL® R 202 VV 90 can be incorporated into the polypropylene glycolmarkedly more rapidly than AEROSIL® R 202, with approximately comparableTheological properties and oil separations.

The hydrophilic fumed silica AEROSIL® 200 is not suitable for theproduction of a polypropylene glycol-based cable gel, because the oilseparation of 97% in that case is much too high.

1. Cable gels, characterized in that they contain, in addition topolypropylene glycol and polyol, from 1 to 15 wt. % of a compressedfumed silica which has been rendered hydrophobic with silicone oil. 2.Use of the cable gels according to claim 1 in the production of glassfibre cables.
 3. A cable gel composition comprising at least one of apolypropylene glycol and a polyol and from 1 to 15 wt. % of a compressedfumed silica which has been rendered hydrophobic with a silicone oil. 4.The cable gel composition according to claim 1 wherein said silica has atamped density of from 60 to 150 g/l.
 5. The cable gel compositionaccording to claim 4 wherein the tamped density of the silica is 90 g/l.6. The cable gel composition according to claim 1 further comprising anantioxidant.
 7. The cable gel composition according to claim 6 whereinthe antioxidant is a mixture of an N-phenyl aniline reaction productwith 2,4,4-trimethylpentene and diphenylamine.
 8. A glass fiber cableproduced from the cable gel composition of claim 1.